dollenberg



Aug 1l, 1959 F. P. DoLLr-:NBER f 2,899,585

SPARK PLUG 'INVENTOR 'folle n ker? F l d Nov. 27, 1957 A Ahn. i

SPARK PLUG Frederick P. Dollenberg, Philadelphia, Pa.

Application November 27, 1957, Serial No. 699,381

8 Claims. (Cl. 313-143) This invention relates to a novel spark plug for internalcornbustion engines and more particularly to a surfacegap-type spark plug which is so constructed that the spark passing between the electrodes thereof moves across a semi-conductive surface.

More particularly, it is an aim of the present invention to provide a spark plug of the aforedescribed character which, due to the novel construction of the center electrode thereof, is capable of utilizing a ceramic core including an annular skirt portion having a radial thickness at the end of the plug across which the spark travels which is Very slight compared to the diameter of the center electrode.

A further object of the invention is to provide a spark plug the shell of which, forming the ground electrode, includes circumferentially spaced segments, surrounding the sparking end of the center electrode and the end of the insulator skirt which is disposed therearound, to provide slots which will prevent the trapping of gases within the shell and thus provide better fuel propagation.

A further object of the invention is to provide a spark plug wherein the sparking tip of the center electrode and the apron portion of the ceramic insulator surrounding said tip are eccentrically disposed relative to the surrounding nose end of the shell to cause turbulence in the gases entering the shell cavity which produces a scouring action.

A further object of the invention is to provide a novel means of mounting the center electrode in the ceramic insulator or core whereby the electrode is unsupported in the core adjacent the sparking tip of said electrode so that breakage of the insulator will be avoided enabling use of an insulator having a minimum wall thickness at the spark plug nose.

Still a further object of the invention is to provide spark plug wherein the skirt portion of the insulating core which surrounds the sparking tip of the center electrode is impregnated with a material to render said insulator portion semi-conductive.

Various other objects and advantages of the invention will hereinafter become more fully apparent from the following description of the drawing, illustrating a presently preferred embodiment thereof, and wherein:

Figure 1 is an end elevational View on an enlarged scale of the spark plug, looking toward the nose end thereof;

Figure 2 is a longitudinal sectional view, partly in elevation, of the spark plug, taken substantially along a plane as indicated by the line 2 2 of Figure l, and

Figure 3 is an enlarged radial sectional view in detail, taken substantially along a plane as indicated by the line 3-3 of Figure l.

Referring more specifically to the drawing, the spark plug in its entirety is designated generally 5 and in ygeneral comprises a shell 6, a central electrode 7 and a ceramic insulator 8.

The shell 6 includes an annular externally threaded body portion 9 from which projects a frusto-conical nose ice portion 10 constituting a second electrode which is provided with circumferentially spaced radially extending slots 11, as seen in Figures l and 3, which slots 11 open through the annular inner face 12 of the nose 10 and divide said nose into four corresponding segments 13, 14, 15 and 16. The body portion 9 and nose 10 form a chamber 17 Iwhich is restricted from the inner end thereof toward the cylindrical Wall portion 12. The outer portion 18 of the shell 6 is enlarged relative to the inner portion 9, 10 thereof and is provided with a cylindrical chamber 19 which is substantially larger than the chamber 17 and which connects therewith by a frusto-conical chamber portion 20. The shell portion 18 has an inclined annular upwardly and inwardly facing shoulder 21 at the lower end of the chamber 19 and a part of said body portion 18 is provided with external ribs 22 forming cooling fins.

The ceramic insulating core 8 includes an outer portion 23 which may be of any desired exterior shape and size and has an enlarged intermediate portion 24 and an inner end portion 2S. The intermediate portion 24 is sized to iit so as to have clearance in the outer chamber 19 of the shell and is provided with an inclined annular shoulder 26 at its lower end which is disposed substantially parallel to the shoulder 21. An annular dished sealing gasket 27 lits conformably between the substantially parallel shoulders 21 and 26. The upper part of the intermediate insulator portion 24 is provided with an annular downwardly and outwardly inclined shoulder 28 on which is disposed an upper annular downwardly and outwardly inclined sealing |gasket 29. The open upper end 30 of the shell 6 is crimped inwardly against the upper sealing gasket 28 for securing the intermediate insulator portion 24 in the outer shell chamber 19 and for compressing the gaskets 27 and 28 so that the insulator 8 is clamped in the shell 6 between the shoulder 21 and the crimped outer shell portion 30.

The inner end portion or skirt 25 of the insulator 8 extends from the inner end of the intermediate portion 24 longitudinally through the shell portion 20 and the shell chamber 17, and is of substantially reduced cross sectional size relative to said intermediate portion 24 and is tapered externally towardits terminal end or nose portion 31 which is disposed within the shell nose 10.

A bore extends longitudinally through the insulator 8 and includes an end portion 32 extending longitudinally through the apron portion 25 of the insulator and into the intermediate portion 24, and an intermediate bore portion 33 which forms a continuation of the bore portion 32 and extends through the remainder of the intermediate portion 24 and through a part of the outer insulator portion 23. The bore portion 33 is disposed in alignment with the bore portion 32 and is of larger diameter than said lbore portion 32. The opposite end of the bore is formed by an internally threaded bore portion 34 which opens through the outer end of the insulator S.

The center electrode 7 includes an elongated spindle 35 of electrical conducting material which extends substantially through the bore portions 32 and 33 and which is provided with an annular crimped portion 36 which bears against the annular shoulder 37 which is disposed around the end of the bore portion 33 which communicates with the bore portion 32. The space between the portion of the spindle 35, which is disposed 1n the bore portion 33, and the wall of said bore portion 33 is filled with a cement 38 for anchoring the spindle 35 immovably in the bore portion 33. The diameter of the bore portion 32 is somewhat greater than the diameter of the spindle 35 (preferably approximately .004 of an inch larger) so that said spindle portion has a clearance in the bore portion 32. The center electrode includes a threaded stem 39 of electrical conductingima- 3 terial which threadedly engages the bore portion 34 and which has a conventional tip 40 disposed beyond the outer end of'the insulator 8 and which is adapted to be engaged by a conventional conductor wire connector, not shown. A spring 41 of electrical conducting material is disposed in the bore portion 33 and has itsends bearing against adjacent ends of the spindle 35 and stem 39 to complete the center electrode 7 and form an elec- As best illustrated in Figure 3, the insulator nose 31 is of substantially uniform external diameter and is of relatively slight radial thickness as compared to the diameter of the spindle 35. Furthermore, this radial thickness is considerably reduced at the distal end of the nose 31 by the ared bore portion 43. The insulator nose 31 is impregnated with carbon so that it constitutes a semi-conductor of electricity.

In the actual assembly of the spark plug a guide collar, not shown, is positioned within the opening 12 of the nose 10 to receive the tip of the insulator nose 31.

The bore or opening of this collar is eccentric relative to the periphery thereof so that the tip of the insulator Anose 31 is eccentrically disposed with respect to the annular Wall 12 when the shell 6 is secured to the insulator 8 by crimping the shell end 30. of this guide collar the insulator nose 31 Vand the spindle tip 42 are disposed nearer certain ofthe nose segments than other of said nose segments. For example, as seen in Figure l, the nose 31 and spindle tip 42 are disposed nearer the portion of the wall 12 forming a part of the segment 16 than the wall portion 12 which forms apart of the segment 14. It will also be noted that the diameter of the spindle 35 is quite large as compared to the external diameter of the insulator Thus, after removal nose 31 and the diameter of the opening 12, the diameter 'of said spindle preferably being approximately twothirds the external diameter of the nose 31 and considerably more than half the diameter of the opening 12, all of which features are of importance in connection with the eflicient operation of the plug 5.

While surface-gap-type plugs as distinguished from the conventional air-gap-type spark plug have beenproduced in the past, such spark plugs have not been successful because the wall thicknesses of the insulator noses were much greater as compared to the diameter of the center electrode than in the spark plug 5. This was found necessary in order to prevent breakage of the insulator. The present invention overcomes this objection in the surface-gap-type plug by forming the center electrode of end sections connected by the spring 41 so that the center electrode will setA up no stresses or strains on the apron portion of the insulator and which would cause breakage of the insulator. This result is further realized through the securement ofthe spindle 35 only inthe bore portion 33 which is surrounded bypan insulator body portion of substantial thickness, and with the spindle part which is contained in the bore portion 32 of the apron 25V being disposed with a slight clearance between the bore wall 32V and the spindle so that no pressure is exerted by the spindle on the apron 25 even if a slight distortion of said spindle portion should result dueto heating of the spindle. VAs a consequence' of the foregoing the spindle 35Qis much larger in` diameterV (approximately .125 of,V ari inch) than the center electrodes of previously' const ructed'surface-gap-type spark plugs. Consequently, vthe spindle 35 is capable of dissipating heat more readilyy and thus remaining cooler while the spark plug is in operation than would be possible if the spindle were of smaller diameter.

Due to the thin characteritic of the Wall of the insulator nose 31, especially the portion thereof surrounding the flared bore surface 43, said insulator nose heats very rapidly and thus prevents an accumulation of carbon between the insulator nose 31 and the annular wall surface 12 of the shell nose. Impregnation of the insulator nose 31 with carbon causes the llame to pass more readily across the tip of the nose from the electrode tip 42 to the shell nose 10, which also is effective in rapidly heating the insulator nose to preventformation of carbon thereon.

Whereas conventional spark plugs produce a weak spark across a gap of approximately .030 of an inch, the spark plug 5 provides a solid llame across a substantially wider gap between the electrode tip 42 and the shell wall 12. As a result, a more complete burning of the combustion mixture is accomplished producing increased power and eiciency in connection with a cylinder of an internal-combustion engine in which the spark plug 5 is employed and which as a consequence effects substantial saving in fuel consumption and a considerable reduction in carbon accumulation in the cylinder and which causes overheating, preignition and numerous other results detrimental to an engine and its operation.

By providing the slots 11 in the nose 10 the trapping of the combustion gases in the chamber 17 is reduced Vto a minimum which results in improved fuel utilization.

Due to the offsetting of the electrode 31 relative to the shell nose 10, the eccentric shape of the space between the insulator nose 31 and wall 12 creates a turbulence of the gases in the chamber 17 which produces a desirable and effective scouring action of the wall of the chamber 17 and the exterior of the apron 25. Y

Various modifications and changes are contemplated and may be resorted to, without departing from the function or scope of the invention as hereinafter defined by the appended claims. i

I claim as my invention:

l. A spark plug comprising an elongated hollow shell of electrical conducting material having an outer end and an inner end, an elongated insulator having an enlarged intermediate portion secured in the outer end of the shell and an inner end portion, of reduced cross sectional size relative to the intermediate portion, disposed in the inner end of the shell and spaced therefrom, said'insulator having a central bore extending longitudinally therethrough, a central electrode mounted in and extending substantially through said bore, a distal part of the inner end of said shell constituting a shell nose and including a substantially cylindrical wall surface of reduced cross sectional size relative to the remainder of the shell and de tiningthe open inner end of the shell, said shell nose constituting a second electrode, the inner extremity of said insulator comprising an insulator nose surrounded by and spaced from said cylindrical wall surface of the shell nose, said central electrode having an inner/end disposed within and surrounded by the insulator nose, and Ithe thickness of the wall of the insulator nose being substantially less than one-half the width of the inner end of the central electrode.

2. A spark plug as in claim 1, said linsulator nose being impregnated with an electrical conducting material and constituting a semi-electrical conductor.

3. A spark plug as in claim l, the bore of said insulator being flared adjacent the extremity of the insulator nose, `said inner end of the central electrode terminating intsaid flared bore portion and being spaced slightly from the extremity of the insulator nose. y

4. A spark plug as in claim 1, said shell providing a chamber around the inner end of the insulator, said shell 1108 being fruSto-conical and having circumferentially spaced radially extending slots opening through said cylindrical wall surface and communicating with the shell chamber, said shell chamber being closed except for the slots `and the open inner end of the shell.

5. A spark plug as in claim 4, the inner end of the central electrode and said insulator nose being eccentrically disposed within said cylindrical Wall surface for causing a swirling of the combustion gases within said chamber of the shell for scouring said chamber and the exterior of the inner end of the insulator.

6. A spark plug as in claim 1, said insulator bore including an intermediate portion extending through the enlarged intermediate portion of the insulator and which -s of larger dia-meter than an inner end portion of said bore which extends through the inner end of the insulator, said central electrode having a portion disposed loosely in said enlarged bore portion, bonding means surrounding said portion of the central electrode for anchoring the central electrode to the insulator, and the portion of said central electrode disposed in said restricted bore portion being of a cross sectional size less than the cross sectional size of said restricted bore portion and being supported for loose fitting engagement therein by said bonding means.

7. A spark plug as in claim 6, said central electrode portions comprising end portions of a spindle forming a part of the central electrode, said central electrode including a stem anchored in and projecting from the opposite outer end of the insulator and having an inner end spaced from the spindle, a spring of electrical conducting material disposed between land bearing against the adjacent ends of the stem and spindle to prevent strains and exure forces being imparted from the stem to the spindle to avoid breakage of the inner end of the insulator.

8. A spark plug as in claim 1, said insulator nose comprising a substantially cylindrical Wall impregnated with an electrical conducting material constituting a semielectrical conductor, the inner end of said central electrode being circular in cross section and having a radius substantially greater than the thickness of the wall of the insulator nose, the bore of said insulator being ared adjacent the extremity of the nose thereof, and said inner end of the central electrode terminating in said flared bore portion and vbeing countersunk slightly relative to the extremity of the insulator nose and shell nose.

References Cited in the file of this patent UNITED STATES PATENTS 1,962,669 Parkin June 12, 1934 2,394,865 McCarthy Feb. l2, 1946 2,548,170 Moth Apr. 10, 1951 2,578,754 Smits Dec. 18, 1951 2,609,808 Bynchinsky Sept. 9, 1952 2,723,364 Ciprani Nov. 8, 1955 

